1. Field of the Invention
The present invention relates to a plug-in power supply for supplying a consumer with a low voltage, and in particular to a plug-in power supply wherein the mains plug unit is exchangeable in the form of a conversion plug system.
2. Description of the Related Art
Plug-in power supply units in the lowest power range are nowadays increasingly built as switching mode power supply units. Due to their small dimensions and their low weight, they have established themselves in many fields of application and they replace the traditional linear devices. By means of the switching mode power supply technology, a so-called universal input voltage input can easily be realized so that the power supply unit can, as far as its electronic concept is concerned, theoretically be operated at each power socket in the world. This, however, is prevented by the great differences existing worldwide between the plug systems and plug shapes, this has the consequence that unsafe so-called plug adapters have to be additionally used in most cases; due to the enlarged distance between the plug-in power supply and the power socket, these plug adapters may increase the torque, which acts on the power socket, in an inadmissible manner.
Hence, the implementation of an exchangeable conversion plug, which is integrated in the design of the device, is a much safer and therefore desirable alternative.
German patent DE 43 22 086 C2 discloses a plug-in power supply for supplying electric devices with low voltage, wherein contacting between the device and the conversion plugs takes place via spring contacts, the respective spring contacts being accommodated in the plug and being in contact with the voltage transformer module of the power supply unit via contact surfaces on the circuit board of the power supply unit. This solution is, however, comparatively complex, since two springs are required per plug version and since the mains plug units must additionally be implemented such that they each consist of two plastic components, viz. the plug contour and a cover, so as to guarantee the touch protection demanded. These parts must be interconnected by means of a precise supersonic welding process, and, in the case of non-optimum welding, the insertion and separation forces between the plug and the plug-in power supply will increase to unacceptable values. Furthermore, the plug unit is not safely locked. It follows that the solution according to this publication is complex, expensive and it offers only a limited process reliability.
U.S. Pat. No. 6,320,353 B1 discloses the implementation of a plug system according to IEC 320 for establishing a contact between a plug-in power supply and an exchangeable mains plug unit. This solution, however, requires for each plug the implementation of a complete socket with two spring contacts per plug and it partly requires stamped and bent components for establishing the connection between the spring contacts and the plug pins. Furthermore, the plug housing is here again bipartite so that the necessary touch protection can be guaranteed. Hence, also this construction is comparatively complex and expensive.
Reference U.S. D454,537 S discloses a solution wherein the electric contact between the device and the plug is established by means of two spring contacts, which are arranged in the housing. The number of springs required is reduced in this way. The plug is oriented parallel to the longitudinal side of the device. The spring contacts are here exposed and may twist in the case of inappropriate treatment. Due to the fact that the plug is pushed on in longitudinally arranged guide means, two slots having a width of approx. 4 mm and a length of approx. 20 mm are formed in the plug. The dimensions of these slots exceed the admissible values of the maximum opening width, according to which the maximum dimensions must not exceed 1.8 mm×4.8 mm. It follows that the structural design shown in this document violates the relevant regulations on electric shock protection.
Furthermore, a locking engagement is established via a plastic spring, which is integrated in the device in question, in the arrangement shown in this publication, said plastic spring including, however, openings to the circuit board, i.e. it only has a limited ESD resistance. Moreover, the plug components for the UK plug each consist of two plastic parts, and this makes the structural design again comparatively complex and expensive.
The Taiwanese publication TW421366Y discloses an arrangement with comparatively broad spring contacts in the housing, said spring contacts being arranged transversely to the longitudinal side. The plug is here connected to the housing in that it is first introduced in a slotted guide means and then pushed on along the housing. Contacting is effected through long longitudinal slots in the plug (approx. 2.5×30 mm) directly onto the plug pins. The dimensions of these slots exceed the admissible values of the air and creepage distances. It follows that also in the case of this structural design, the relevant regulations on electric shock protection are violated. A locking engagement is guaranteed by a separate locking bar with an additional spring. Also in this case, the implementation of the plug housing is bipartite for all plug embodiments, i.e. also this structural design is comparatively complex and therefore expensive.
The published international patent application WO 2004/013937 A1 discloses a plug coupling wherein an exchangeable mains plug is arranged on the housing of a plug-in power supply, the housing having provided thereon a protruding guide web with contact elements and the mains plug being provided with a complementary cavity for accommodating the guide web. The guide web is provided with a recess and the mains plug has arranged thereon a complementary pin for locking engagement with said recess, so that, by means of a suitable movement of the mains plug relative to the housing, the mains plug can be fixed to the housing and a connection can be established between the contact elements of the mains plug and the contact elements of the guide web.
However, the plug coupling according to this reference is disadvantageous insofar as it does, on the one hand, not comply with the relevant standards with regard to air and creepage distances and insofar as, on the other hand, unlocking of said plug coupling is comparatively difficult to realize.